Are you kidding? The minis in this set look amazing by comparison to most of what was around in the red-box era.
And plastic minis? There weren’t any. Lead is where it’s at.
The first plastic minis I can remember being available were in the latter part of the 1980s which I suppose is still just about Red Box era but they were mostly miniatures for other games. The first ones I ever came in contact with was Citadel Miniatures/Games Workshop’s offerings. I genuinely can’t remember any others.